Constructional element and method for its manufacture

ABSTRACT

Constructional element intended for cogged joining having side walls of a single wooden or wood-like element; preferably both side walls are made of solid wood. Each element is preferably furnished with longitudinal grooves on its inside, curved across its longitudinal axis and on its inner side coated with a layer of plastic material, preferably thermoplastic material, which may also partially or completely surround ribs that hold the curved side walls in a stable position. The invention also concerns a method for the manufacture of the constructional element as well as a method for the manufacture of structural elements that constitute complete side walls of such a constructional element.

The present invention concerns a constructional element intended forbuilding with logs with cogged joints, hereinafter generally referred toas notching, as well as a method for the manufacture of such element.

The invention further concerns a method for the manufacture of astructural element intended to be part of a constructional elementaccording to the first aspect of the invention, or in otherconstructional elements. The structural element may also be used as anindependent product.

BACKGROUND

It is an old tradition to raise buildings with timber logs. In recentyears this tradition has mainly been upheld with respect to building ofcabins/ leisure buildings. Cabins with cogged joints are generally seento be particularly beautiful. Building with this tradition is, however,not free of problems.

A disadvantage with notching of cabins/ buildings in real timber is thehigh requirement of premium quality timber. Such timber is today ascarce resource and the buildings therefore become expensive. Anotherdisadvantage is the specific thermal insulation. Compared to wellinsulated buildings of modern construction, the thermal insulation issignificantly poorer. In a Nordic climate, notched buildings that arenot provided with an internal insulation is not suited for use all year,and is quite uneconomical also for cabin use.

A third disadvantage is related to the fact that buildings in timberlogs sinks several per cents (cm per meter height) the first years,which leads to severe problems with respect to maintaining tight doors,doors that do not get jammed and to maintain leakage free roof openingsfor pipes and ventilation.

On this basis and on the basis of a need for a more extensive use ofrecycle material in building production, attempts have been made withrespect to make a constructional element that looks like real timber butconsists of an internal, insulated core and a wooden or wood-like“shell”.

Norwegian patent No. 311 583 describes timber-like elements for notchingwhere each side of the elements is comprised by several (e.g. 3) joinedpanel elements that are profiled in a manner so that their outer sidessubsequent to the joining appear as substantially continuous, convexsurfaces. Between these joined panel elements spacer elements arearranged that serve to hold the panels in a steady, unchanged mutualdistance from each other. The same spacer elements serve to give theentire building its required strength. The void between the outer partsis intended to be filled with a thermally insulating material, e.g.polyurethane. Near the ends the elements are provided with recesses fornotching. The construction has the disadvantage that preparing andassembling of each timber-like element from individual panels andspacers is a comparatively complex process.

Swedish laid-open publication No. 457 456 describes a “timber-element”with outer tree panels provided with longitudinal groves, where thespacers are arranged in the groves. The void between the panels and thespacers are also in this construction intended to be filled with athermally insulating material like foamed polyurethane. Holes arearranged in certain positions of the spacers so that rods 8 may bepositioned (vertically) through the holes in each element of a completedwall, whereby said rods may constitute the weight carrying elements ofthe wall. Like for the construction discussed above, this constructioncomprises a lot of components that need to be adapted to each other. Itis quite a “puzzle” work to put together one single timber element fromits separate components.

U.S. Pat. No. 4,433,519 describes a hollow, cylindrical prefabricatedconstructional element intended for the same use as the above mentionedpublication. Here it is assumed that the convex outer surfaces arecomprised either by glass fibre, metal, plastic or moulded woodenproducts with the required structural integrity. The outer panels arethus not made in a natural wooden material. Flanges at the upper andlower side of the constructional elements are arranged to overlap whenthe elements are placed on top of each other, and they are provided withholes so that bolts or the like may be inserted through the elements tolock the elements together. Like the previously discussed constructionsthis one also comprises spacer elements that are arranged at certainintervals along the elements, but here the prefabricated elementsthemselves are designed to carry most of the weight load. The voidbetween the elements is preferably filled with a thermally insulatingmaterial. This construction has the advantage over the previous onesthat it is assembled from fewer components but on the other hand theside panels are not in “whole wood”.

Swedish laid-open publication No. 440 250 describes still anotherproduct intended for notching, and it constitutes outer wooden panelswith inner spacers that are attached to the side panels by means oflongitudinal grooves in the latter. A wooden panel according to thispublication does not comprise a convex outer surface. It is mentioned,however, that the edges may be chamfered to give a visual impression ofsuch a convex surface.

OBJECTIVES

It is an object of the present invention to provide a constructionalelement and a method for the manufacture of such an element, whichvisually and in assembled state gives an optimal impression of notchedtimber logs.

It is thus an object of the present invention to provide aconstructional element with convex outer surfaces in “whole wood”, whichmay be manufactured in a quick and rational process.

It is furthermore an object to provide a constructional element of saidtype with the required volume for all thermal insulation in an innervoid, and which is simple to insulate with conventional fibrous orfoamed insulation materials before or after assembly to a building.

THE INVENTION

Said objects are achieved by a constructional element and the methodaccording to the invention as further elaborated below.

According to a first aspect the invention concerns a constructionalelement as defined by claim 1 and a method for the manufacture of suchan element as defined by claim 12.

According to another aspect the invention concerns a structural elementthat constitutes: a side wall of the constructional element according tothe first aspect of the invention as defined by claim 18 and a methodfor the manufacture of such an element as defined by claim 22.

Preferred embodiments of the invention are disclosed by the dependentclaims.

A central aspect of the present invention is the fact that thecomponents constituting a constructional element are assembled in asimple and rational process that may be largely automatized. It is afurther important aspect that said objects are achieved withoutcompromising the aesthetical aspects of the product which has sides inwhole wood. The process of making grooves on one side (the inside) ofthe boards removes tension in the boards and in addition the groovesprovide a mechanical grip for the plastic material. By the option to“lock” the side edges of the boards when they are bent to a curvedshape, a controllable degree of cracks are formed, thus making theboards look even more like real timber logs. It is an alternative to usea thermosetting plastic material instead of a thermoplastic material,requiring an alternative technique for application that is alsodescribed in detail.

Furthermore it is preferred that the side walls are based on panels ofreal (whole) wood, even though materials like fibreboard panels andother tree-like materials may also be used. It is also possible to useone material for the outside wall and a different material for theinside wall. It is even feasible to use an even simpler type of panelfor the inner wall, e.g. one that is not convex and if it is not desiredto give the impression of real timber logs inside, the panels for theinside walls may have a flat surface that subsequently may be coveredwith wall paper or the like. In this latter case a structural elementmanufactured as defined by claim 12 is used for the inside panel of theconstructional element and a structural element manufactured as definedby claim 11 is used for the outside panel of the constructional element.

CONCRETE EMBODIMENTS OF THE INVENTION

The invention will now be described in further detail with reference tothe enclosed drawings, wherein,

FIG. 1-6 show vital steps of the manufacture process for aconstructional element.

FIG. 7 is a schematic illustration of the process comprising the stepsshown in FIGS. 1-6.

FIG. 7 b is an enlarged partial view of a variant of the process shownin FIG. 7.

FIGS. 8 and 9 are two different side sectional views of a completedconstructional element according to the present invention.

FIG. 10 is a sectional side view of a wall comprised by constructionalelements according to the invention.

FIG. 11 is a cross sectional view of two constructional elements of theinvention, one placed on top of the other.

FIGS. 12 and 13 show steps of manufacture for parts of a constructionalelement according to the invention in a case where a thermosettingplastic material is used instead of a thermoplastic material.

FIG. 1 shows an end view of a board 1 for forming a structural elementthat constitutes a side surface (wall) of a constructional elementaccording to the invention. The side that is faced down will form anoutside of the constructional element while the side that is faced upand provided with a number of longitudinal grooves 2, will form aninside of the constructional element.

FIG. 2 shows the board of FIG. 1 at a stage where rolls (not all shown)on all sides of the board have begun to force the board into a curvedshape in a direction cross the board's longitudinal direction.

FIG. 3 shows the board in the final curved shape, in the manner it isfed into an extruder.

FIG. 4 shows the board as emerging from the extruder. A thermoplasticmaterial fills the grooves 2 in the board's inner (concave) side andforms a coating a few mm thick on this side. Close to the side edges ofthe board the same thermoplastic material forms two longitudinal flanges4 a and 4 b whose function are explained below. Polypropylene andpolyethylene are preferred thermoplastic materials and preferably highdensity polyethylene. PVC is also a well suited plastic material.

FIG. 5 shows the board subsequent to having been furnished with a rib 5in the still soft thermoplastic material on the concave side of theboard 1. The rib 5 is sideways delimited by the flanges 4 a and 4 b.Such ribs 5 are arranged at even intervals in the longitudinal directionof the board. The term “rib” is used instead of “spacer” to emphasizethat the function of the rib is to hold the board stable and curved, notmerely to hold/ define the distance between the boards of a completedconstructional element. A similar function is not included in any one ofthe previously known constructional elements, which is why theseprevious elements do not provide such a close resemblance to real timberlogs. When using ribs that is cut from a single plate or board, it willbe understood that the orientation of the rib on the board will besubstantially perpendicular to the longitudinal direction (axis) of theboard. When later referring to the “ends” of the ribs, the parts of theribs close to the flanges 4 a and 4 b in FIG. 5 is what is meant.

As shown by FIGS. 5 and 6 the ribs may have recesses 6 intended to befilled with additional thermoplastic material in a subsequent step (FIG.6). Alternatively the ribs 5 are fully covered by a thin layer ofthermoplastic material. Each rib is preferably furnished with two holesfor reception of pegs corresponding to the pegs used in the furnitureindustry for assembly of furniture. The holes are preferably localizednear each end of the ribs (near the longitudinal flanges 4 a, 4 b), andat a right angle with the longitudinal direction of the structuralelement, such that one and the same peg may be received by a hole in arib attached to a structural element that forms part of an exterior wallsurface and by a hole in a corresponding rib attached to a structuralelement that forms part of an internal wall surface, therebycontributing in binding together the inner and the outer structuralelement of a constructional element.

FIG. 7 shows the entire process schematically. Boards are fed from leftin the Figure between pairs of rolls A. With reference to FIG. 7 theentire process is described in relation to the treatment of a singleboard. Grooves 2 in the board 1 may be formed at an earlier stage butmay conveniently be made at this stage of the process. The grooves maybe solely longitudinal, as such grooves are the simplest to make, orthey can have other shapes or patterns, such as a diamond-shapedpattern. Alternatively the grooves may be omitted. The rolls B causes aninitial curving (bending) of the board as shown in FIG. 2, while theboard at the point of entering the extruder C has been given its finalcurved shape as shown in FIG. 3. Prior to covering the board's concaveside with plastics in the extruder, it is preferred to treat this sidewith an adhesive agent or a compatibilizer that makes the plasticmaterial bind better to the wood. Such an adhesive agent may be maleicanhydride. As an alternative to the shown pair of rolls A and B theboard may be fed by means of an articulated belt.

An endless belt 19 is furnished with fixtures 18 to which the ribs aretemporarily attached. At point D the ribs are forced against the side ofthe board 1 that has been covered with a layer of thermoplastic materialin the extruder. If the ribs are provided with holes the holes may beused for an exact positioning of the ribs relative to the board on whichthey are to be attached. Immediately thereafter, at the point E in FIG.7, each rib 5 receives thermoplastic material in through openings of therib, fed to it in by injection moulding so that the thermoplasticmaterial sticks to an inner surface of the rib as well as to the stillsoft thermoplastic material 3 on the board 1. Alternatively, as shown inFIG. 7 b, each rib is forced against the board in an enveloping die 18′that follows the endless belt 19, and at point E a thermoplasticmaterial is injected through a conduit 20 to cover the entire rib 5completely with thermoplastic material. FIG. 7 b also shows how a layerof an adhesive agent 21 is fed to the board 1 immediately prior to theaddition of thermoplastic material 3 in the extruder C.

Coolant air is blown over the thermoplastic material 3 and the ribs 5 atthe point F so that the thermoplastic material sets and ensures apermanent attachment of the ribs to the board, thereby safeguarding apermanent curved shape of the latter. Alternatively water may be used asa coolant, by filling the voids between the ribs with water immediatelysubsequent to the injection moulding. The water is sucked up again atthe point where the product element (structural element) is about toleave the belt/ production station.

It is convenient to use wooden ribs as wood is quite dimensionallystable in the direction of the fibres, and maintains its shape even whenexposed to severe temperature variations over a long time. It is mostimportant that the ribs are dimensionally stable across the longitudinaldirection of the constructional element, which will mean in the verticaldirection for the common use if the elements. It is otherwise notrequired with any kind of refinement of the wood used for ribs,non-planed wooden boards may be used and it does not matter if there areknots or holes from knots in the boards. Also other materials may beused for the ribs, like steel, synthetic materials and compositematerials, but it is hard to find materials with the positive propertiesof wood without adding costs to the production. When using steel ribsthey may be provided with spikes that penetrate the board to which therib is attached. When using a synthetic material or a compositematerial, the ribs may be dimensioned with a larger extension in thelongitudinal direction of the board compared to when using steel orwooden ribs, without increasing the weight of structuralelement/constructional element, as such ribs may be designed asnon-compact structure.

When it is stated that a number of ribs are arranged with definedintervals, this usually means one fixed interval between each rib, eventhough from a productional point of view also other solutions may workequally well.

It will be recognized that with the method described above, which may beautomatized and controlled by a CAD/ CAM system, completed side surfacesor panels for constructional elements may be fabricated in tailor-madedimensions that are limited only by the length of the boards fed to theprocess. With “completed side surfaces” is understood that the boardshave received their final curved shape, the ribs provide the structurewith strength and integrity and the thermoplastic material provide thestructure a moisture barrier. The integral intermediate product thusformed constitutes what is also referred to as a structural element forthe constructional element.

FIG. 8 is a sectional view that illustrates how two side surfacesmanufactured in accordance with the process of FIGS. 1-6 and 7 areassembled to make up a complete constructional element according to theinvention. Attachment means 8 are mounted at upper and lower end of eachrib or some of the ribs with screws or the like, and also to a pipeelement 7. Each constructional element in one and the same wall willhave such pipe elements positioned straight above each other so thatcontinuous rods may be inserted from the uppermost to the lowermostelement of the wall in selected positions. This feature is more fullyexplained with reference to FIG. 10.

It is preferred to use identical attachment means 8 in one and the samebuilding or in one and the same wall. It should be noted, however, thatby simply replacing the attachment means with some of another and largerhorizontal dimension, a thicker constructional element is obtained whichallows room for more thermally insulating material. It is thus notrequired to change the shape or dimension of the ribs to obtain athicker constructional element. This is a feature of importance whencomparing the present invention with constructional elements accordingto the prior art.

FIG. 9 is a sectional view of a constructional element between to setsof ribs. Sealing tape or foil 9 up and down ruining the entire length ofthe constructional element, delimits the internal void of theconstructional element, such that a preferably injected thermallyinsulating material 10, like mineral wool, is kept steady within theelement.

FIG. 10 is a sectional view of a wall 11 notched from constructionalelements according to the invention. At even intervals along the lengthof the constructional elements pipe elements 7 suited to accommodatebolts or rods 14 are arranged as mentioned. Such bolts or rods typicallyextend through the entire height of the wall. Each bolt 14 preferably isprovided with threads at both ends for simple attachment to an anchoringelement 15 in the cement base 16 and (at upper end) e.g. a nut 17,possibly in combination with a washer (not shown).

In practice it is convenient that e.g. the lower end of each pipeelement 7 has a conical tapered shape that fits into the upper end of asimilar pipe element that protrudes somewhat from the constructionalelements, such that the pipe elements during assembly of a wall arepushed into and slightly overlaps each other. In this way the pipeelements lock each constructional element to the adjacent element aboveand below with respect to any sideways movement. By tightening the nuts17 with an appropriate torque a strong and reliable binding of each wallis achieved while the risk of a gradual sinking of the wall is as goodas completely eliminated. Furthermore, as the constructional elementsare very lightweight, they normally need to be secured to the base wallto avoid the risk of being blown away during very heavy winds.

It should be emphasized that it is also an alternative to replace theabove mentioned pipe element by an element that on one hand is able tofunction as a connective element for the two structural elementsconstituting the side walls of the constructional element and on theother hand is able to work as a guide for vertical bolts through anassembled wall. Such alternative elements will be equivalent to the pipeelements described above even if they do not have the shape of a wholepipe.

The wall shown in FIG. 10 has a lower log or half-log 12 in solid woodand a corresponding upper log 13 in solid wood. It is not required withsuch solid wood logs, but it represents a preferred embodiment.

FIG. 11 is a sectional view of two adjacent constructional elementswhich constitute part of a wall. The nethermost ⅔ of the sectional viesis within the body of rib 5 which is provided with holes into which pegs22 are inserted to position the ribs 5 relative to each other in thepairs of oppositely arranged structural elements that form respectivesides of a constructional element. It should be noted that incontradiction to FIG. 8 no pipe element 7 or attachment means 8 isshown. Some of the pairs of ribs require a type of pipe element or thelike that extends in the full height of the wall while other pairs ofribs 5 may be just as shown in FIG. 11. The uppermost ⅓ of the sectionalview is placed between the ribs and shows the insulating material 10 inthe constructional element.

FIGS. 12 and 13 show process steps for the manufacture of structuralelements of the invention where the plastic layer coated to the insideof the boards 1, is a layer of thermosetting plastics rather thanthermoplastics. The choice of material requires that the manufacturetakes place in a press shape mould instead of in an extruder (as shownin FIGS. 7 and 7 b).

FIG. 12 shows an open mould 23 with a lower part 23 a and an upper part23 b, hinged about an axis 24. The upper part comprises a framestructure 24 that holds a hinged, three-part pressing profile 25 a-cwith a shape adapted to the shape of the structural elements to bemanufactured. Between the frame 24 and the pressing profile 25 a-c arearranged hoses 26 for pressurized air. A board 1 is positioned I upperpart 23 b while ribs 5 and epoxy with reinforcement 3′ are positioned inlower part 23 a of the mould.

FIG. 13 shows the forming of a structural element as the mould 23 hasbeen closed and locked with hatch 27. The hoses 26 have been filled withpressurized air causing the hinged, three-part pressing profile,preferably made in aluminium, to apply a significant downwards force tothe entire board. The side of the board that was faced up in FIG. 12 isnow faced down and is pressed to an intimate contact with and thus bindsto the epoxy resin 3′ which is preferably reinforced with glass fibres.As most clearly seen from FIG. 13 only the central part 25 b of thethree-part pressing profile 25 is rigidly connected to the framestructure 24, while the outer parts 25 a, 25 c of the pressing profileare hinged to the central part 25 b with a certain degree of rotationalfreedom, such that the outermost edges of the outer parts 25 a, 25 cunder influence of the hoses filled with pressurised air, in the closedcondition of the mould are moved downwards until the curvature of thepressing profile 25 a-c corresponds to the curvature of the ribs 5.

With respect to the cogged joints, these are preferably not made as anintegral part of the constructional element according to the invention.Rather the constructional elements are terminated with an open recessintended to receive separate cogging elements of the type described inNorwegian patent application No. 1996 3642.

When using separate cogging elements each constructional element isterminated as mentioned with an open end towards the joint. At the openend a pre-fabricated transition-element (not shown) will preferably beattached to the constructional element by means of “speilsveising” orthe like. The outer profile of such a transition-element will have aprofile corresponding to the internal profile of the constructionalelement while the inner profile of said transition-piece is arectangular opening with a shape that corresponds to the outer profileof a cogging or splicing element. After attachment (welding) of thetransition-element to the thermoplastic material inside theconstructional element, the transition-element forms part of a sealedbarrier that prevents moisture from entering the constructional elementfrom an end of same.

When in this description there is made a distinction between a coggingelement and a splicing element, this has to do with the fact that long(outer) walls are divided where an inner wall cross such outer walls.The separating inner wall will include a cogging element (also denotedend element) at the outside of and at a right angle to the outer wall,while a splicing element that is completely hidden by the constructionalelements and the cogging joint, ties together two principally equalconstructional elements of the outer wall that meet at the coggingjoint. These cogging elements and splicing elements are described inNorwegian patent application No. 1996 3642 and do therefore notconstitute part of the present invention. The splicing and coggingelements are preferably made in whole wood, but particularly thesplicing elements that after assembly are invisible, may also be made inother materials.

At terminations of walls towards windows and doors, the constructionalelement is terminated in an end-piece that in contradiction to thetransition-element does not have any opening. The end-piece may, likethe transition-element, be made as a prefabricated thermoplasticelement. The manner for attachment to the rest of constructional elementmay be as for the transition-element, i.e. it may be welded to thethermoplastic material at the inside of the boards by means of“speilsveising” or the like. While otherwise visible parts of thetransition elements are hidden by the cogging joints, the otherwisevisible parts of the end-pieces are hidden behind a door frame, windowframe or the like.

It is worth noticing that at delivery from a factory to a constructionalsite the constructional elements according to the invention will alreadybe furnished with end-pieces and transition-elements as well as separatecogging elements where appropriate. It is also worth noticing that theconstructional element according to the present invention does notcomprise the cogging element.

Extrusion of the plastic material to the board represents a ratedetermining step of the manufacture process and a realistic speed forthis process is about 1 m per minute, which for a relevant log thicknesscorresponds to a production of 10 m² wall per hour or a normal sizedcabin per day.

The list of advantages with the present invention is long.

Firstly the method of manufacture is simple and may readily be automatedand is therefore inexpensive. A normal cabin may be drawn in A CADsystem within an hour's time, be manufactured in 1-2 days and normallybe delivered in less than 2 weeks.

Secondly the applied plastic material constitutes a diffusion proofbarrier that prevents any moisture form entering the void of thethermally insulating material.

A third advantage is the design of the element's walls—with a curvedshape that is mistakenly similar to solid logs.

A forth advantage is the weight. The constructional elements has a ⅓weight of solid logs and still makes a strong wall construction whenassembled. Only ⅓ of the wood needed for a timber cabin is consumed andthe quality of the wood is less critical.

A fifth advantage is the thermal insulation, as the walls are easy toinsulate and an entire wall may be insulated in one single operationwith fibre or foam. Pre-fabricated constructional elements has threetimes the insulating ability of whole timber logs, and is thus at levelwith buildings in framework and mats of mineral wool. The soundinsulation ability is also very good.

As a sixth advantage may be mentioned that supply of electrical power ifdesired may be hidden in the walls.

The production is easy to adapt/ change (tailor-made), whereby anarchitect-designed cabin or the like is read into a CAD/ CAM softwarethat automatically calculates and initiates production of the correctnumber and size of numbered constructional elements. Such elements maybe delivered as a ready to raise building-kit with an instruction-CDthat contains a step-by step explanation of how to best raise the kit.

The properties may be associated with the individual components of apreferred constructional element according to the invention, as follows:

The side walls are wooden or of a wood-like material that provides thedesired look and provides stability in the longitudinal direction of theconstructional element while at the same time allowing sufficient holdfor nails, screws and the like.

The plastic material makes the elements diffusion proof, stabilizes theside walls (the boards) in the cross direction and binds the ribs to theboards.

The ribs provide dimension stability (constant height and curvature) andprovides attachment for the attachment means.

The attachment means decide the thickness of a constructional elementand hold together—aided by the pipe elements—pairs of structuralelements (side walls) thus forming a constructional element.

The pipe elements bind together two and two of said structural elementsto one constructional element, provide the latter a weight carryingability and stable height and contribute to guide the constructionalelements when assembled to a wall. Subsequent to such assembly the pipeelements form guides for bolts or rods that hold the constructionalelements of a wall tightly together.

Tape or foil strips over and under each element in their longitudinaldirection provide a diffusion barrier at these sides of theconstructional element.

Insulating material in the constructional element insulates againsttemperature and sound.

While the structural elements comprising the visible parts of aconstructional element according to the invention are mainly intendedfor assembly in pairs to such constructional elements as discussed inthis description, such structural elements may also be used as forpanelling or cleading. For such a purpose it is convenient but notrequired to provide the side edges with some kind of tongue and grooveor the like to ensure a nice and even transition between each of theelements.

1. Constructional element intended for cogged joining, comprising two structural elements in the form of side walls each of which being based on a single wooden or wood-like board (1) with an inner coating of a plastic material (3), characterized in that the inside of each board (1) is furnished with ribs (5) that make the side walls dimensionally stable, said ribs (5) being attached to the board (1) by means of the plastic material (3), while the constructional element also comprises attachment means (8) that hold said structural elements at a predetermined distance from one another.
 2. Constructional element as claimed in claim 1, characterized in that said plastic material (3) is polyethylene, polypropylene or PVC.
 3. Constructional element as claimed in claim 1, characterized in that said plastic material (3) is a thermosetting plastic, preferably a glass fibre reinforced thermosetting plastic.
 4. Constructional element as claimed in claim 1, characterized in that said ribs (5) are wooden ribs.
 5. Constructional element as claimed in claim 1, characterized in that said ribs (5) are made in steel, a synthetic material or a composite material.
 6. Constructional element as claimed in claim 1, characterized in that the structural elements that constitute the side walls of the constructional element are curved across their longitudinal direction with a convex outer surface.
 7. Constructional element as claimed in claim 1, characterized in that one or more of the boardsforming structural elements are furnished with grooves (2) on their inner side.
 8. Constructional element as claimed in claim 1, characterized in that the means to hold the structural elements in a fixed mutual distance from one another comprise evenly arranged pairs of attachment means (8) attached a one of their sides to a number of all to all ribs (5) of each structural element, and at the opposite side to one for the pair common pipe element (7) that extends vertically through the entire constructional element.
 9. Constructional element as claimed in claim 1, characterized in that at the end or ends facing a cogged joint the constructional element is provided with a transition-element attached in a diffusion proof manner to the plastic material (3), said transition-element having a central opening with an inner shape that corresponds to the outer shape of a cogging element or splicing element.
 10. Constructional element as claimed in claim 1, characterized in that at the end or ends facing a door frame or a window frame the constructional element is provided with an end-piece that is attached in a diffusion proof manner to the plastic material (3).
 11. Constructional element as claimed in claim 1, characterized in that longitudinal slits between the uppermost and lowermost edges of said side walls are sealed in a diffusion proof manner with tape.
 12. Method for the manufacture of a constructional element intended for cogged joining, characterized in that the method comprises i) manufacturing separate structural elements that form side walls of the constructional element in a process where: a) pre-dimensioned wooden or wood-like boards are on one of their sides coated with a layer of a plastic material and optionally furnished with longitudinal flanges of plastic material along both sides of the boards, b) a number of ribs with a size and dimension adapted to the boards are arranged at certain intervals along the longitudinal direction of the boards and attached to the boards with said plastic material in a process of injection moulding, “speilsveising” or pressing, after which c) attachment means are attached in pairs at both ends of at least some of said ribs, whereby the side of the attachment means that is faced away from each respective rib is adapted to be attached to a certain pipe element, and ii) placing together two and two of such structural elements in pairs and attach them to one another by attaching each pair of attachment means to a respective pipe element that thereby forms a bridging connection between each respective pair of structural elements.
 13. Method as claimed in claim 12, characterized in that the boards prior to being coated with a plastic material are furnished with grooves on the side to which the plastic material is to be coated.
 14. Method as claimed in claim 12, characterized in that said plastic material is a thermoplastic material applied by extrusion.
 15. Method as claimed in claim 12, characterized in that said plastic material is a thermosetting plastic material, preferably reinforced with glass fibre, which is applied by means of a press shape mould.
 16. Method as claimed in claim 12, characterized in that each board prior to being coated with a plastic material is bent (curved) across its longitudinal axis to a concave inside and a convex outside and that each rib is provided with a correspondingly curved surface before it is attached to the concave side of the board.
 17. Method as claimed in claim 12, characterized in that the method comprises the additional steps of: iii) attaching particularly adapted transition-elements or end-pieces to each of the two ends of each constructional element, iv) closing the longitudinal slit along the underside of each constructional element with a for that purpose particularly adapted tape or the like, v) filling the otherwise open void between between the side walls of each constructional element with a therefore suited insulating material, vi) closing the longitudinal slit along the upper side of each constructional element with a for that purpose particularly adapted tape or the like, and vii) attaching particularly and per se known cogging elements to the constructional elements by means of the under item iii) mentioned transition-elements where relevant.
 18. Structural element for a constructional element, characterized in that it comprises a wooden or wood-like board (1) a diffusion proof layer of a plastic material (3) that covers one side of the board and a number of ribs (5) attached with defined intervals in the longitudinal direction of the board (1), on the same side as the plastic material (3), for making the structural element dimensionally stable.
 19. Structural element as claimed in claim 18, characterized in that the board is provided with grooves on the side where the plastic is applied.
 20. Structural element as claimed in claim 18, characterized in that the board is curved across its longitudinal direction such that the side covered by a plastic material is the concave side.
 21. Structural element as claimed in claim 18, characterized in that the ribs (5) when having the shape of simple plate elements, are arranged mainly perpendicular to the longitudinal axis of the structural element.
 22. Method for the manufacture of a structural element for a constructional element, characterized in that the method comprises a) preparing wooden or wood-like boards in pre-determined dimensions, b) coating one side of each board with a layer of a plastic material, c) arrange a number of ribs at mutually defined intervals along the longitudinal direction of each board and attach said ribs to the boards with said plastic material in order to provide the structural element with strength and dimension stability.
 23. Method as claimed in claim 22, characterized in that the board prior to the coating is furnished with grooves.
 24. Method as claimed in claim 22, characterized in that each board prior to the treatment defined by step b) is curved cross its longitudinal direction to a concave inside and a convex outside and in such curved position fed to an extruder where the board is provided with a layer of thermoplastic material and that said ribs at the side facing the board has a curvature that corresponds to the curvature of the board.
 25. Method as claimed in claim 22, characterized in that each rib is attached to one side of the board as defined by step c) in a press shape mould after having been coated on the same side with a preferably glass fibre reinforced thermosetting plastic. 